If you haven't done so, yet, I highly recommend you start with the ITIL books, themselves. There's a lot of material there that will allow you to understand implementation.

The fact that you've asked the broad question of "How do I implement ITIL?" is a difficult question to answer, since the answer depends on many factors...

- What's the size of the enterprise?
- What is the number of stakeholders in each role?
- What's the allowable budget?
- Gap analysis of existing processes
- Gap analysis of existing tools
- What is the appetite for success by the client/customer?
- Where is the enterprise currently suffering its greatest pains?
- Is the enterprise trying to fix one discipline or role out many?
- How much time do you have to implement your solutions?
- Etc.

Your firm's best bet is to hire an experienced set of consultants, temporarily, that allow you to work along side them, in their implementation effort. This will allow you to act as an apprentice and learn from them.

There is nothing that says you can't learn on your own, either. I did (back in the beginning of ITIL there were very few people to turn to for help). However, you'll need a firm that allows you a lot of time to learn and implement and who also allows you the luxury to recover from your mistakes, as you do so. If you're implementing for external clients, you may not have these things available to you.

In the end, success is always about knowledge and motivation. Knowledge you get by learning. Learning can start with the ITIL books, which is where I recommend you start.